I have never heard anyone disparage Glenn Miller or his music. He had a unique sound and was distinguishable among the many big bands of his time.
Many of the groups you list are one hit wonders, others are producers of formulaic pop hits—what we called “Bubblegum Music”. Music for early teens and pre-teens.
Starship was a desperate attempt by Grace Slick and Thumper to keep what was left of Jefferson Airplane together. The Airplane was a hard act to follow and Starship was seen as bad copy of a great seminal group of what became known as the San Francisco Sound of the mid to late Sixities. Drugs and fatigue had also taken their toll on the original members.
I liked the fusion of jazz and rock produced by Steely Dan. It was new at the time, but they were buried on pop radio by one-hit copycat groups and forever associated with them.
Barry Manilow, although an accomplished singer and songwriter, was a product of American advertising and commercialism at a time when that was very uncool. He appealed to the older generation, not his own. He produced safe pop (mostly for the aging WWII crowd) and although that will make money, it won’t make great music. I compare him to “The Archies”. Bubblegum Music for an older generation.
Michael Bolton and Kenny G. were also accomplished, but produced easy listening music, not necessarily great music. They produced Muzak. Nothing edgy, seminal or anything that will become classic.
Like the above, the rest are good at what they do, but they will hardly be referenced as distinguished in the future.